Ammonium-N increased from 2.3 g/L to an average of ∼3.0 g/L
with the sequential batch digestion, which are at the lower end of
the reported inhibitory range from 1.7 to 14 g/L [27]. Ammonium-N
concentrations thatinhibit methanogenesis vary due to differences
in substrates, inocula, environmental conditions (e.g. temperature,
pH), and acclimation periods [28]. Based on the corresponding
increase in biogas production rates and the average methane yield
of 123 ± 15 m3 per tonnes of dry waste (equal to 95% of the long
term biochemical methane potential yield), it is unlikely that
ammonium-N caused any significant inhibition in this study.